What determines the tilt angle of a precessing proton in a magnetic field? Is it a constant the assuming no additional magnetic forces? In an NMR a perpendicular magnetic field is applied which rotates the precessing magnetic moment into the X-Y plane. After this perpendicular magnetic pulse is removed the magnetic moment returns back to its original tilt angle. This runs counter to the spinning top analogy that is often used for the precessing proton. My understanding is that the tilt angle of a precessing top will remain fixed assuming no friction. So If I took a spinning top precessing at angle θ1 and then applied a force to increase the tilt angle to θ2, when that force is removed the top will continue to precess at this new tilt angle θ2. Is this all correct? Why is the proton different from the top in this case?